The present invention relates to a diaphragm type damper for reducing pulsations of fluid pressure, and particularly to a diaphragm type damper for reducing pulsations of high pressure fluid.
There is generally known a pulsation absorbing device for absorbing pulsations of fluid in a fluid passage. For example, a bladder type accumulator falls under this sort of pulsation absorbing device. The bladder type accumulator, which uses a rubber diaphragm, has a problem in that high pressure gas sealed in a back pressure chamber penetrates through the diaphragm to leak. In addition, the bladder type accumulator has a drawback in that it has a large size and a heavy weight.
On the other hand, Japanese Utility Preliminary Publication No. Hei 5-1854 discloses fuel supply equipment provided with a diaphragm type accumulator (diaphragm type damper) for reducing pulsations.
A high pressure gasoline pump, to which a conventional damper is fitted, has a structure as shown in FIG. 11. A plunger 105 is driven by a cam 103 to reciprocate. A discharge passage for discharging fuel, which is pressurized in a pressurizing chamber 107, is connected with a pressure chamber 111 of a high pressure damper 109. The pressurized fuel (high pressure fuel) has its high pressure pulsations damped in the high pressure damper 109, and then it is discharged. Incidentally, in FIG. 11, a low pressure damper 113 is provided on the side of an intake passage for introducing fuel from an intake port. The low pressure damper 113 is used for reducing pressure pulsations for low pressure fuel, and reduces low pressure pulsations by using a helical spring 115.
As shown in FIG. 12, the high pressure damper 109 is formed by having a metal diaphragm 121 interposed between an upper half body 117 and a lower half body (pressure chamber member) 119, and seals high pressure gas in a back pressure chamber 123 defined by the upper half body 117 and the diaphragm 121. Between the lower half body 119 and the diaphragm 121 is formed a pressure chamber 127. The diaphragm 121 faces the pressure chamber 127 and reduces pulsations in the pressure chamber 127. The high pressure damper 109 is conventionally formed by interposing the diaphragm 121 between the upper half body 117 and the lower half body 119 and welding those three members together at a welding portion 129.
In the above described welding structure of the welding portion 129, heat capacity at the time of welding needs to be made as small as possible so that the three members can be welded together from the outside. Therefore, marginal portions of the upper half body 117 and the lower half body 119 (in the welding portion 129) are made as thin as possible. However, because of this thin formation of the welding portion 129, when the pump is operated, a force coming from the high pressure gas sealed in the back pressure chamber 123 and the high pressure fluid acts on the welding portion 129 in such a manner so as to urge the welding portion 129 to open as indicated by an arrow A in FIG. 12 (bending moment). This bending moment A causes mechanical fatigue at the welding portion 129 where the half bodies 117 and 119 are thinner which leads to damage and/or leakage.